### Secrets in the Pigpen
Codes at War · Pigpen
In the eighteenth century, a secretive group called the Freemasons needed a way to keep their messages hidden. Later, Union prisoners of war during the American Civil War used the exact same trick. Instead of swapping letters for other letters, they swapped letters for pictures.
To use the pigpen cipher, you draw four grids. The first two look like big tic-tac-toe boards, and the second two look like giant X's. You drop the alphabet into the empty spaces of these grids, adding a single dot to every space in the second board and the second X.
Here is the trick: every letter becomes the shape of the "fence" around it. To write a secret message, you just draw the lines that surround your letter. If your letter lives in a dotted grid, you draw the fence and put a dot inside it.
Check out the demo grids next to this story to see how the alphabet fits inside the pens. A codebreaker just draws the blank grids, matches the shapes to the letters, and reads the hidden word!
